The use of polytetrafluoroethylene as an additive to enhance properties of elastomers or plastics has been a long-sought goal because such blends have improved properties such as tear, flame or abrasion resistance over those of the base resin. However, because fibrils and agglomerates of polytetrafluoroethylene (PTFE) ordinarily develop when PTFE is subjected to shear forces during compounding with other resins, the resulting blends are nonuniform and may show excessive modulus and have warping problems. Furthermore, due to the fibrillation and agglomeration, blends which contain known polytetrafluoroethylene resins are difficult to prepare and process especially at high additive levels.
The incorporation of fluoropolymers such as polytetrafluoroethylene and such polymers modified with comonomer into elastomers or thermoplastics has been attempted before. High molecular weight, non-melt-processible polymers of tetrafluoroethylene, including those which contain small amounts of comonomers such as hexafluoropropylene, tend to draw out into fibers, or fibrillate, when sheared. Although it is a useful property for some applications such as paste extrusion onto wire, this fibrillation causes problems when the polytetrafluoroethylene or modified polytetrafluoroethylene is to be incorporated into an elastomer or a thermoplastic. The fibrillating tetrafluoroethylene polymer forms visible agglomerates and results in undesirable increases in modulus when incorporated into elastomers. When compounded into thermoplastics, the fibrillating tetrafluoroethylene polymer causes undesirable melt swell when the polymer melt is forced through an orifice such as the die at the end of an extruder. The addition of melt-processible fluorocopolymers such as Teflon.RTM. FEP or PFA fluorocarbon resins or low molecular weight, irradiated PTFE, to elastomers or thermoplastics avoids the problems of fibrillation but this approach does not improve certain properties of the elastomer or thermoplastic.